Materials in single crystal form play a role in various device applications such as, e.g., semiconductor and, in particular, semiconductor optical devices. Examples of such optical devices are light emitting diodes, laser diodes, optical detectors, opto-isolators, and phototransistors as described, e.g., in the book by A. A. Bergh et al, Light Emitting Diodes, Clarendon Press, 1976. Devices may typically comprise a substrate and one or several deposited epitaxial layers, substrate and layers being rendered semiconducting or semi-insulating by the presence of appropriate dopants such as, e.g., S, Se, Sn, Zn, Te, Cd, Cr, or Fe. Among materials considered to be particularly suitable for optical device applications are doped and undoped III-V compounds.
The manufacture of device substrates typically involves cutting a single crystal boule which may have been produced by controlled solidification from a melt. Among controlled solidification techniques, pulling from a melt has proved particularly effective for III-V compounds such as, e.g., indium arsenide, gallium arsenide, gallium phosphide, and indium phosphide. In some instances, pulling may be carried out under atmospheric conditions; in others, pulling is preferably carried out under elevated pressure and from a melt whose surface is protected by an immiscible liquid. Apparatus for carrying out such socalled Liquid Encapsulated Czochralski growth has been disclosed by a number of authors and, in particular, by J. B. Mullin et al, "Liquid Encapsulation Crystal Pulling at High Pressures", Journal of Crystal Growth, Vol. 4 (1968), pp. 281-285; K. J. Bachman et al, "Liquid Encapsulated Czochralski Pulling of InP Crystals", Journal of Electronic Materials, Vol. 4 (1975), pp. 389-406; R. L. Henry et al, "InP Growth and Properties", Journal of Electronic Materials, Vol. 7 (1978), pp. 647-657; E. Buehler, "Simple Pressurized Chambers for Liquid Encapsulated Czochralski Crystal Growth", Journal of Crystal Growth, Vol. 43 (1978), pp. 584-588, the latter giving details of construction and operation of apparatus.
Achieved considerable advance in the development of crystal pulling methods notwithstanding, reliability of methods remains a concern in the reproducible preparation of single crystals. One concern, expressed for example by A. J. Marshall et al, "Growth of InP Crystals by the Synthesis Solute Diffusion Method", Journal of Crystal Growth, Vol. 44 (1978), pp. 651-652, is the formation of twinned crystals in the course of pulling from a melt.